my $letters = '[a-zA-Z]'; # try - maybe the character range will work for you. It works in Cyr-1521, but does not in KOI8-R
my @wordpatterns = map { qr/(?<!$letters)(\Q$_\E$letters*)/ } qw(tak het hen toj);

while (my $next_line = <$FH>) {
    foreach my $pattern (@wordpatterns) {
        my $count_words = ($next_line =~ s/$pattern/>$1</gi);
    }
}